Substance use prevention is a public health priority. The medical, economic, and social impacts of substance abuse cost Americans half a trillion dollars annually. This study has broad public health significance by addressing a distinct pathway between aggression and substance use that has been resistant to treatment. This study will integrate mindfulness into an evidence-based prevention program, Coping Power (CP), and test the feasibility of the Mindfulness-Enhanced Coping Power (CP-ME) program with children who have high levels of reactive aggression (RA) and are thus at high risk for early substance use. CP is based on a contextual social-cognitive model of risk, targeting malleable child- and family-level risk factors for substance use and aggression through separate child and parent intervention components. Eight randomized controlled trials demonstrate CP's effectiveness in reducing proactive aggression (PA) and substance use. However, CP has not produced significant reductions in reactive aggression (RA), which has a distinct pathway to substance use. This innovative study seeks to improve CP's effects on RA by infusing the child and parent interventions with mindfulness strategies (yoga, meditation, and breath awareness). Mindfulness is theorized to increase emotional, cognitive, and behavioral self-regulation and to improve the ability to direct attention to the present moment. A growing evidence base shows that mindfulness can improve these mechanisms, which are linked to RA. The specific aims of this study are to: Aim 1: Adapt the CP child and parent intervention components by integrating mindfulness strategies (CP-ME), with input from mindfulness and CP practitioners, research experts, and children and parents participating in a pre-test; Aim 2: Conduct a feasibility pilot with 96 child/ parent dyads to: (a) evaluate the feasibility and acceptability of the CP-ME intervention; (b) obtain preliminary evidence favoring CP-ME relative to standard CP. The feasibility pilot will compare CP-ME and CP with 5th grade students who have high levels of teacher-rated RA and their parents (N=96 parent/child dyads; 48 randomly assigned to CP-ME, 48 to CP). We hypothesize that CP-ME will be as feasible to implement as CP and will yield equivalent or better intervention fidelity, quality, and acceptability ratings. We also hypothesize that, in comparison with standard CP, CP-ME will evidence greater effect sizes (ES) for RA and its active mechanisms targeted by mindfulness (Child: attentional capacity; emotional, cognitive, and behavioral self- regulation; physiological reactivity. Parent: attentional capacity; self-regulation; warmth; positive discipline). The integration of mindfulness into CP represents a unique effort to bridge conceptual and programmatic strengths of a cognitive-behavioral intervention with mindfulness strategies to reduce RA, which has a distinct pathway to substance use and is resistant to change. The investigative team includes researchers with in- depth experience in Coping Power, adaptation of evidence-based programs, substance use prevention, and mindfulness. Results will be incorporated as preliminary data for a subsequent larger R01 efficacy trial.